Image pick-up tube support structure for semiconductive target

ABSTRACT

An image pick-up tube with a diode array target having a chemically deposited silicon resistive film covering the diode array of the target and a target mounting assembly including a conductive ring having an inwardly extending flange adjacent one end of the ring. The flange has a window or face plate side in sealing engagement with a face plate and a target side which is grooved to receive the periphery of the diode array target. The inner wall of the ring coacts with the ring flange to form a notch for a spring type retaining ring. The retaining ring when properly positioned within the notch directs the periphery of the diode array target into the groove and retains the target firmly within the groove of the conductive ring. The target bearing side of the flange is channeled to prevent air entrapment between the target and face plate when vacuumizing the image pick-up tube. The end of the ring opposite the face plate surface forms a seat for the bulb of the image pick-up tube and a stop for a retaining ring positioning tool. The stop properly positions the target retaining ring when carried by the tool and prevents the retaining ring from contacting the fragile diode array target. When assembled with the target the conductive ring provides the electrical contact for biasing the target and taking off the video signal.

United States Patent [191 Sadler [451 Apr. 3, 1973 [541 IMAGE PICK-UPTUBE SUPPORT STRUCTURE FOR SEMICONDUCTIVE TARGET [75] Inventor: PorterSadler, Dallas, Tex.

[73] Assignee: Texas Instruments Dallas, Tex.

[22] Filed: June 1, 1971 [21] Appl. No.: 148,762

Incorporated,

[52] US. Cl. ..313/66, 313/288, 313/283 [51] Int. Cl ..H0lj 29/02,l-IOlj 31/38, H0lj 29/45 [58] Field of Search.....3l3/65 A, 65 AB, 65 T,65 R,

Primary ExaminerRobert Segal Attorney-Harold Levine, James 0. Dixon,Andrew M. Hassell, Melvin Sharp, Gary C. Honeycutt and Alva H. Bandy[57] ABSTRACT An image pick-up tube with a diode array target having achemically deposited silicon resistive film covering the diode array ofthe target and a target mounting assembly including a conductive ringhaving an inwardly extendingflange adjacent one end of the ring. Theflange has a window or face plate side in sealing engagement with a faceplate and a target side which is grooved to receive the periphery of thediode array target. The inner wall of the ring coacts with the ringflange to form a notch for a spring type retaining ring. The retainingring when properly positioned within the notch directs the periphery ofthe diode array target into the groove and retains the target firmlywithin the groove of the conductive ring. The target bearing side of theflange is channeled to prevent air entrapment between the target andface plate when vacuumizing the image pick-up tube. The end of the ringopposite the face plate surface forms a seat for the bulb of the imagepick-up tube and a stop for a retaining ring positioning tool. The stopproperly positions the target retaining ring when carried by the tooland prevents the retaining ring from contacting the fragile diode arraytarget. When assembled with the target the conductive ring provides theelectrical contact for biasing the target and taking off the videosignal.

6 Claims, 4 Drawing Figures PATEtm-imPRa 1915 sum 2 0r 2 PHOTONSDEPLETION REGION IMAGE PICK-UP TUBE SUPPORT STRUCTURE FOR SEMICONDUCTIVETARGET BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to an image pick-up tube and more particularly to animage pick-up tube having an improved diode array target and targetsupporting assembly.

2. Description of the Prior Art In the past, image pick-up tubes havehad a hybrid type electron gun with magnetic deflection andelectrostatic focus. This design was to allow the axis ofthe camera tobe brought closer to the axis of the display tube, thereby reducing theparallax error. Electronic zoom has been accomplished simply by holdingthe deflection currents fixed and varying all electrode voltages exceptthe accelerator voltage proportionally. The accelerating mesh potentialwas therefore varied between 400 to 1,000 volts to vary the raster areaby ratio of 2.5 to 1. Operation of this tube revealed that this modeproduced severe raster burn-in which manifests itself as changes in thetube dark current. An antimony trisulphide target, which behaves as asimple photoconductor, was used as the target for the electron gun. Ithas a relatively high dark current and a variable gamma (degree ofcontrast in the image) less than unity, both of which gives rise to poorlow light level performance and dynamic range. The antimony trisulphidetarget is readily damaged during operation by raster burn, accidentalphotoconductor or photoemitter light burn, or thermionic cathode slumpdue to ion burn and other causes. Also because ofits instability atelevated temperatures above 120C the tube cannot be baked at thedesirable high temperatures to reduce the dark current. Dark current isof importance to tube operation as it limits the low light levelcapability of the tube by introducing shading and noise. Antimonytrisulphide was replaced by gallium arsenide but the target was found tohave undesirable aging characteristic effects-It also has been thepractice to pressure fit the target to a face plate of the image pickuptube using an indium ring. The indium ring was segmented to permit theevacuation of air which would otherwise be trapped between the targetand face plate when the tube was air evacuated. However, a targetmounted in this fashion was found to have unacceptable performance dueto the harmonics generated in the target which was not held firmly bythe segmented indium rings. In this configuration the face plate wasattached to the bulb. In attaching the bulb, care had to be exercisedthat the bulb material when melted did not contact and damage thetarget. Further the tube output had to be taken from the target throughthe bulb; when connecting the output lead to the target the fragiletarget was often broken.

SUMMARY OF THE INVENTION It is an object of this invention to provide arugged image pick-up tube which may be constructed using convenientfabrication procedures.

It is another object of this invention to provide an image pick-up tubehaving slow aging characteristics.

It is still another object of this invention to provide an image pick-uptube which is repairable.

It is a further object of this invention to provide an image pick-uptube constructed of materials compatible with high temperature bakingprocedures for improving tube performance.

It is yet another object of this invention to provide an image pick-uptube which has a low dark current, high light sensitivity in bothvisible and infrared spectrums and unity gamma.

In accordance with the invention, there is provided an image pick-uptube, suitable for use with an VIDICON type electron beam scan devicesuch as, for example, an all magnetic, or an all electrostatic, orhybrid, or inverse hybrid type structure for directing a beam ofelectrons from an electron gun to a silicon diode array target having achemically deposited silicon resistive sea capable of withstanding tubebake-out temperatures of up to 400C. The target is mounted in the tubeusing a retractable target mounting technique. The mount holds the thinsilicon target in a manner that avoids strain and distortion which ifpresent generate noise in the output signal of the tube, and alsopermits replacement of the target when its performance isunsatisfactory. In addition the target mount is in electrical contactwith the target and the power supply and video signal take off circuitcan be connected to the target mount thereby enhancing the ruggedness ofthe tube.

BRIEF DESCRIPTION OF TI-IE'DRAWINGS FIG. 1 is a cross-sectional view ofthe embodiment of this invention.

FIG. 2 is a partial cross-sectional view of the target and a schematicdiagram of the target biasing circuit and video output signal circuit.

FIG. 3 is an exploded. isometric view of the image pick-up tube targetsupporting assembly.

FIG. 4 is an isometric view of the target electrode ring disclosingdetails of the target supporting side of the ring.

A detailed description of a preferred embodiment of this inventionfollows with reference being made to the drawings wherein like partshave been given like reference numerals for clarity and understanding ofthe elements and features of the invention.

Referring to FIG. 1, the image pick-up tube 10 construction of thepresent invention comprises a tubular housing or bulb 12 having a pinplug-in base 14 at one end and a target supporting assembly 16 at itsother end. The pin plug-in base 14 may be, for example, any type basecompatible with the plug-in socket used in a camera package and capableof withstanding tube bake out temperatures up to 400C. The bulb 12houses a cathode 18 of an electron gun which when heated by heater 20emits electrons through a beam forming grid 22. The electron beam isaccelerated and focused as it passes respectively through an acceleratorgrid 24 and a focusing grid 26 on its way to a decelerating grid 28. Thedecelerating grid 28, often referred to as the decelerating mesh, isprovided to decrease the velocity of the beam electrons reaching atarget 30. The image pick-up tube utilizes magnetic focus and deflectionof the electron beam which is provided by a horizontal and verticaldeflection coil 32 and a focusing coil 34. The deflection coil 32 andfocusing coil 34 together with a beam alignment coil 36 are positionedwithin a pre-aligned camera package (not shown) to provide a propertarget 30 scanning beam in the tube when it is operated in the camerapackage.

The target 30 is a diode array target which as shown in FIG. 2 is asilicon diode array target having, for example, an N conductivity typesubstrate 40. An N conductivity type layer 42 about 1,500 A thick isformed over the incident light side of the target 30 by phosphorousdiffusion. This N -layer 42 enhances the collection efficiency ofphotoexcited holes, particularly at the short wave length end of thevisible spectrum and thus enhances the blue sensitivity of the imagepick-up tube 10. In addition the N -layer 42 provides a gettering actionfor some impurities which significantly enhances the dark currentperformance of the silicon diode array target 30. The side of thesubstrate 40 opposite the N -film side has a silicon oxide (SiO layer 44which may be formed thereon by the thermal oxidation technique. A diodearray having a density of about 620,000 diodes per square centimeter isformed through the silicon oxide layer 44. BY using wellknownphotoresist techniques the diodes are formed by diffusing, for example,boron into the N-type doped silicon substrate 40 to form P-type islands46. The diode bearing surface is then covered overall with a thinresistive film 48, commonly referred to as a resistive sea. This film 48is essential to a silicon diode array target, because without it, theoxide potential can charge below cathode potential and act as a coplanargrid preventing the electron beam from landing on the diodes. Theresistive sea 48 is a layer of a chemically deposited silicon with athickness of about 1,000 A and a sheet resistivity of about 10 to 10ohms per square. The method of forming this chemically deposited siliconlayer is disclosed in co-pending application Ser. No. 139,068 filed Apr.30, 1971 by Victor Harrap for an Improved Diode Array Vidicon. Imagepick-up tubes having resistive seas formed in accordance with theteachings of this application will operate satisfactorily with up to 650volts on the decelerating mesh 28.

The target 30, FIG. 1, is mounted in the target support assembly 16sealed to the end of bulb 12 opposite the plug-in end 14. The targetsupport assembly, FIGS. 1 and 3, comprises a conductive ring 50 havingadjacent one end an inwardly extending flange member 52 adapted toreceive on one side, hereinafter referred to as the window side, awindow or face plate 54. The face plate 54 may be constructed of glassor other suitable radiation transmitting material. A suitable glass, for

example, for visible and near infrared wavelengths is a borosilicateglass having a composition of SiO 80 percent, B 0 14 percent, Na O 4percent, and A1 0 02 percent. Suitable glass is sold by Corning asCorning No. 7052. In order to form a reliable seal under thermal andmechanical stress between the ring 50 and the hard glass face plate 54it is necessary that the conductive ring 50 be made of a conductivematerialhaving a thermal coefficient of expansion which matches that ofthe hard glass. An iron-nickel-cobalt alloy having a composition ofiron-54 percent, nickel-29 percent, and cobalt-l7 percent sold under thetrademark KOVAR has substantially the same coefficient of expansion andtherefore matches the thermal coefficient of the hard glass, Corning No.7052, sufficiently to form a reliable vacuum proof seal. However, anyhard glass-metal seal should perform satisfactorily if the differentialcalibration between the thermal coefficients of expansions is less than100 parts per million. The opposite side of the flange 52, hereinafterreferred to as the target side, is provided with a groove 56 adjacent tothe edge of the flange 52. The inner wall 58 on the target side of theconductive ring is sloped inwardly at an acute angle with the targetside of flange 52 to form a notch for a spring type retaining ring 60.The retaining ring 60 may be made of any suitable material such as, forexample, nickel or a nickel-chromium alloy sold under the trademarkNichrome which will not lose its elasticity as a result of electronbombardment and operating temperatures. With the target 30 positionedwith its peripheries extending over the groove 56, the spring retainingring 60 may be compressed for insertion to the conductive ring 50 whereit is released to expand into the notch and force the periphery of thetarget 30 into the groove 56. To prevent air from being trapped betweenthe face plate and the target, the conductive ring 50 is constructedwith grooves 64 (FIG. 4) preferably four in number, across the targetbearing side of the flange 52 so that the area between the face plate 54and target 30 (FIG. 1) is in communication with the area of the bulb.With this target supporting assembly the target is held firmly to avoidstrain and distortion within the target. The bulb 12 is sealed to a seat62 formed on the end of the target side of the conductive ring 50. Theseat 62 is sufficiently wide to accommodate the thickness of the glasstube 12 and provide an inwardly extending stop member for the purposehereinafter described. The bulb 12 is preferably made of a hard glassmaterial such as, for example, the Corning No. 7052 glass previouslydescribed which has a coefficient of expansion matching that of theKOVAR conductive ring 50 to which it is sealed.

A special tool (not shown) is used to insert or retract the springretaining ring 60 (FIGS. 1 and 3) into the conductive ring notch withoutdamaging or breaking the thin silicon target 30. This tool has a lengthlonger than the bulb 12 and a cross section corresponding to the crosssection of the bulb 12. It has a spring retaining ring carryingmechanism on one end adapted to engage the retaining ring 60 firmly anda manipulating handle on the other end for actuating the retaining ringcarrying mechanism to compress the ends of the retaining ring 60 forinsertion into or removal from the conductive ring 50 notch through thebulb 12. The outer periphery of the tool forms a flange area adapted toengage the stop of the conductive ring 50 to limit insertion of the tooland to properly position the retaining ring carrying mechanism forretaining the retaining ring or releasing it into the notch withoutbreaking the target 30.

With the target support assembly 16 sealed to the bulb 12, the target 30in place, and the grids and elec-.

tron gun electrically connected to the pins of the plugin base 14, thegrids and electron gun are inserted into the bulb 12 and the base 14sealed to the bulb 12. The image pick-up tube may then be baked to atemperature up to 400C and air evacuated from the bulb 12 to form avacuum.

For operation the pin type plug-in base 14 is inserted into acorresponding plug-in socket of a camera package preferably havingvoltage-regulated supplies or filament transformers as no change in suchpower supplies is required. As the target 30 is in electrical contactwith the conductive ring 50, a signal electrode is attached to theconductive ring 50 (FIG. 2) for taking the video signal off the targetbetween the ring contact and a load resistor 66. The load resistor isalso connected to a source of power 68 for biasing the target positivewith respect to the cathode. In operation the target 30 receives thepreviously described low energy electron beam passing through thedecelerating mesh 28 in a scanning mode. Since the substrate of thetarget is about volts positive relative to the cathode, the electronbeam will deposit electrons at the diodes charging them to cathodepotential. The diodes will remain charged until the depletion layercapacitance, which is a measure of the diode charge storing capability,is discharged by light created minority carriers, (holes) or by diodeleakage. The holes generated at the light incident surface are sweptacross the depletion region to the diode P-type region and contribute tothe leakage current. Recharging of the diode by the electron beamcreates the desired video signal at the video amplifier load resistor66. Since all the holes reaching a diode during a scan time contributeto the discharging of the diode, the signal is proportional to theintegrated local photon flux.

Although a preferred embodiment of the invention has been describedherein, it will be apparent to the person skilled in the art thatvarious modifications to the details of construction shown and describedmay be made without departing from the scope of this invention.

What is claimed is:

1. An image pick-up tube comprising:

a. an evacuated housing:

b. an electron beam producing device in one end of the housing operativeto produce a target scanning electron beam;

c. a substantially circular target comprising a semiconductive substratemounted in the other end of the housing operative responsive to lightfalling on one side to forma charge pattern on another side; and

d. an electrically conductive target supporting means supporting thetarget in the path of the target scanning electron beam, said targetsupporting means including (i) a cylindrical support member having aportion of reduced diameter for receiving said other end of said housingto form a sealed longitudinal extension thereof, the support memberfurther having an internally extending flange, (ii) a substantiallycircular face plate at least partially within said support member andsealingly engaging said flange, (iii) a groove adjacent the edge of theinterior side of the flange receiving the perimeter portion of thetarget and making electrical contact therewith, and (iv) a targetretaining spring in substantial contact with said groove thereby tosecure the target to the electrical conductive member whereby the targetis supported without strain or distortion and the electricallyconductive target supporting member forms a target output and biasingcontact. 2. An image pick-up tube according to claim 1 wherein saidtarget is a silicon diode array target having a chemicallydepositedsilicon resistive sea over all the diodes and 81110011 dioxide layer forpreventing charge accumulation on the silicon dioxide layer and loss inresolution.

3. Am image pick-up tube according to claim 1 wherein said targetretaining means is a retractable spring.

4. Am image pick-up tube according to claim 1 wherein said targetincludes a silicon substrate of one type conductivity, a more heavilydoped film of the same type conductivity diffused on one side of saidsubstrate for enhancing the collection efficiency of photoexcited holes,a plurality of islands of conductivity type opposite that of thesubstrate diffused within the opposite side of the substrate through asilicon oxide layer for forming an array of diodes in the siliconsubstrate, and a high resistivity film covering the diode bearingsurface of the substrate for preventing charge accumu lation on thesilicon dioxide layer and loss in resolution. 5. Am image pick-up tubeaccording to claim 4 wherein the silicon substrate is of N conductivitytype.

6. An image pick-up tube according to claim 1, wherein the targetsupporting side of the support member flange of the electricallyconductive target supporting means includes a plurality of groovesextending across the target supporting side of said flange -to provide aplurality of passages in communication with the area formed between theface plate and target and the remaining area of the housing.

1. An image pick-up tube comprising: a. an evacuated housing: b. anelectron beam producing device in one end of the housing operative toproduce a target scanning electron beam; c. a substantially circulartarget comprising a semiconductive substrate mounted in the other end ofthe housing operative responsive to light falling on one side to form acharge pattern on another side; and d. an electrically conductive targetsupporting means supporting the target in the path of the targetscanning electron beam, said target supporting means including (i) acylindrical support member having a portion of reduced diameter forreceiving said other end of said housing to form a sealed longitudinalextension thereof, the support member further having an internallyextending flange, (ii) a substantially circular face plate at leastpartially within said support member and sealingly engaging said flange,(iii) a groove adjacent the edge of the interior side of the flangereceiving the perimeter portion of the target and making electricalcontact therewith, and (iv) a target retaining spring in substantialcontact with said groove thereby to secure the target to the electricalconductive member whereby the target is supported without strain ordistortion and the electrically conductive target supporting memberforms a target output and biasing contact.
 2. An image pick-up tubeaccording to claim 1 wherein said target is a silicon diode array targethaving a chemically deposited silicon resistive sea over all the diodesand silicon dioxide layer for preventing charge accumulation on thesilicon dioxide layer and loss in resolution.
 3. Am image pick-up tubeaccording to claim 1 wherein said target retaining means is aretractable spring.
 4. Am image pick-up tube according to claim 1wherein said target includes a silicon substrate of one typeconductivity, a more heavily doped film of the same type conductivitydiffused on one side of said substrate for enhancing the collectionefficiency of photo-excited holes, a plurality of islands ofconductivity type opposite that of the substrate diffused within theopposite side of the substrate through a silicon oxide layer for formingan array of diodes in the silicon substrate, and a high resistivity filmcovering the diode bearing surface of the substrate for preventingcharge accumulation on the silicon dioxide layer and loss in resolution.5. Am image pick-up tube according to claim 4 wherein the siliconsubstrate is of N conductivity type.
 6. An image pick-up tube aCcordingto claim 1, wherein the target supporting side of the support memberflange of the electrically conductive target supporting means includes aplurality of grooves extending across the target supporting side of saidflange to provide a plurality of passages in communication with the areaformed between the face plate and target and the remaining area of thehousing.